1. Field of the Invention
The present invention generally relates to a metal/ceramic bonding article having a ceramic substrate and a metal plate bonded to the ceramic substrate, a method for producing the same, a metal/ceramic bonding substrate using the metal/ceramic bonding article, and a power module assembled by using the metal/ceramic bonding article. More specifically, the invention relates to a metal/ceramic bonding article wherein it is difficult to produce cracks in a ceramic member even if thermal shocks are repeatedly applied thereto, a method for producing the same, a metal/ceramic bonding substrate using the metal/ceramic bonding article, and a power module assembled by using the metal/ceramic bonding article.
2. Description of the Prior Art
In a metal/ceramic bonding article used as an insulating substrate, cracks are easily produced in a ceramic member by thermal stress due to differential thermal expansion which is caused between the ceramic member and a metal member by thermal shocks after bonding. As a method for relaxing such thermal stress, there is known a method for decreasing the thickness of the peripheral portion of a metal member, i.e., a method for forming a stepped structure or fillet in the peripheral portion of a metal member.
In order to realize such a structure, there is proposed a method for forming a fillet by utilizing the difference in etch rate between a brazing filler metal and a metal member, the brazing filler metal including silver as a matrix for bonding a metal member to a ceramic member (see Japanese Patent Laid-Open No. 10-326949).
However, in this method, it is difficult to control the dimension of the stepped portion and/or fillet. That is, it is difficult to freely change the width and thickness of the stepped portion and/or fillet, and it is difficult to provide a metal/ceramic bonding article which is higher reliable with respect to repeated heat cycles.